Restrictor valve for a servomotor circuit



July 6, 1954 w ERNST 2,682,748

RESTRICTOR VALVE FOR A SERVOMQTOR CIRCUIT Original Filed April 3; 1951 RI R2 28 i a uuuu 2m Patented July 6, 1954 RESTRICTOR VALVE FOR A SERVOMOTOR CIRCUIT Walter Ernst, Dayton, Ohio, assignor to The Thompson Grinder Company, Springfield, Ohio, a corporation of Ohio Original application April 3, 1951, Serial No. 219,039. Divided and this application April 12,

1952, Serial No. 282,013

9 Claims.

This invention relates to hydraulic servomotor systems and to methods of operation thereof, and particularly to an automatic restrictor valve adaptedfor being placed in such a servo- 2 Referring to the drawing somewhat more in detail, the arrangement illustrated in Figure 1 comprises a bed or frame It on which is slidably mounted a table 12. The bed and table may motor circuit. represent, for example, a grinding machine This application is a division of my co-pehding wherein the table i 2 is the part that supports application, Serial No. 219,039, filed April 3, 1951, the work piece to be operated. and assigned to the same assignee as the instant Mounted in bed i0 is a hydraulic cylinder l4 application. in which is reciprocal a piston It having the rod In servo-motor systems of any type, it is necesportions l8 and 20 extending opposite ways sary to arrive at a compromise between sentherefrom. Rod I8 is connected for reciprocatsitivity and stability. This comes about because ing table i2 on bed It. in an extremely sensitive servo-motor system the For supplying pressure fluid to cylinder It on part that is moved at the output side of the systhe opposite sides of piston it there is provided tem will have a tendency to overrun the part that a pump 22 connected for drawing fluid from a is moved at the input side. With a system, on reservoir 24 and discharging the said fluid to a the other hand, that is extremely stable this pressure conduit 26. tendency is eliminated but, at the same time, a 7 Pressure conduit 26 leads to the inlet port great deal of accuracy of adjustment is lost. of a servo valve, generally indicated at 23, and

Having the foregoing in mind, the present inwhich is more fully disclosed and described in vention has as its primary object the provision of my co-pending application referred to above.

a servo-motor system, particularly a hydraulic The servo valve 28 also comprises an exhaust system, which is extremely stable in operation line 30 leading back to reservoir 24 and the servbut which, at the same time, is also extremely ice conduit 32 leading to the left end of cylinder sensitive. It, and service conduit 3d leading to the inlet A particular object of this invention is the port of a valve comprising a body 36 and having provision of an automatic restrictor valve for a an outlet port connected by conduit 38 with the hydraulic servo-motor system, which will operright end of cylinder I 4. ate to permit rapid movement of both the input The servo valve 28 is of the type having a and output members of the system, but which valve member for controlling flow from conduit will prevent overrunning of the input member 26 to the service conduits 32 and 34 and also for by the output member. controlling the flow from the service conduits to A still further object is the provision of a the exhaust conduit 30. A hand wheel it! is m h f p r in a y r ulic rv -m t r provided for rotating the valve member for resystem by which increased sensitivity and stabilversibly connecting the service conduits with the ity are obtained. pressure and exhaust conduits.

These and other objects and advantages be- The servo valve is of the follow-up type and come more apparent on reference to the followcomprises a sleeve connected with pinion 52 that ing specification taken in connection with the is engaged by rack 44 connected to reciprocate accompanying d W with table l2. The arrangement is such that a Figure 1 is a more or less diagrammatic plan predetermined adjustment of the valve member view of a hydraulic servo-motor system accordof the servo valve will be accompanied for a ing to my invention associated with a load to be corresponding amount of movement of table 12. moved thereby. I In the type of machine tools with which a Figure 2 is a diagrammatic representation of 45 servo-motor mechanism according to my inventhe elements of the servo-motor system of Figure 1; and,

Figure 3 is a sectional view indicated by line tor valve of this invention.

tion is most useful, the table [2 and the work members mounted thereon represents a substantial mass and for this reason once set in motion, has considerable inertia and will, therefore, have a tendency to overrun the position 3 in which it is to be halted if it approaches the said position at a high speed.

At the same time, it is many times desirable to adjust the table l2 at a high rate of speed and if the servomotor system is normally so adjusted as to prevent the overrun of the table, it will be so sluggish that a rapid adjustment of the valve member of the servo valve will permit the servo valve member to overrun the table, whereby control over the table is entirely lost.

In order to provide for rapid adjustment or" table [2 and, at the same time, to prevent the overrunning thereof, I provide the valve having a valve body 36 into which conduit 34 1eads from the servo valve and from which conduit 38 leads to the right end of cylinder I4.

In Figure 3 it will be noted that valve body 36 has a valve bore 46 therein which comprises a central chamber 48 and the interconnected end chamber 50. A valve member 52 is reciprocal in bore 46 and includes the reduced diameter center part 54 and the outwardly tapering portions 55 that connect central part 54 with the end spools 58 that fit closely in bore 46.

The ends of the valve member comprise stems 69 extending into the pilot cylinders 62 so that pressure fluid conducted to the pilot cylinders will act on the ends of the stems.

Within each pilot cylinder there is a spring 64 bearing between the outer closed end of the pertaining cylinder and a washer 66 that rests on a shoulder formed on the stem.

The springs 64 thus serve as centering springs for normally retaining the valve member in its centered position.

Each pilot cylinder has an adjustable abutment screw 8 for stopping the valve member at a predetermined shifted position.

The central chamber 48 in the valve body communicates with interconnected chambers 59 by means of a bore it adapted for being variably restricted by adjustable needle valve 12.

Connected with each of the pilot cylinders is a pilot conduit 14 and the pilot conduits are connected with the service conduits 32 and 34 at a position therealong close to the point where the service conduits connect with the servo valve 28.

Reference to Figure 3 will serve to reveal that whenever fluid pressure in a sufiicient amount is delivered to either one of the pilot cylinders 62 the valve member 52 will be shifted from its centered position, thus establishing a by-pass around bore H1 and thus reducing the restriction offered to fluid flow from conduit 38 to conduit 34 or vice versa.

The illustration in Figure 2 diagrammatically shows the manner in which th servomotor system; according to the present invention, operates. In this view the conduits correspond to those in Figures 1 and 3 and the servo valve 28 is represented by the bridge arrangement of resistors. y

In Figure 2 resistor Rl represents the passage in valve 23 between conduit 26 and conduit 34; R2 represents the passage between conduits 26 and conduit 32: R3 represents the passage between conduit 34 and exhaust conduit 3|]; and R4 represents the passage between conduit 32 and exhaust conduit 30.

When valve 28 is adjusted one of the resistors R2 and RI will be decreased and the other simultaneously increased and the one of the resistors, R3 or R4 directly opposite the increased resistor will be also increased and the other thereof decreased. This adjustment effects a pressure change between conduits 32 and 34 which brings about movement of piston I6 and its connected parts until the original condition of balance within valve 23 is restored.

In normal operation, valve member 52 of the automatic restrictor valve remains in its centered position and creates a predetermined restriction to fluid flow to or from cylinder [4 in either direction of movement of piston I6 thereof, thereby damping movements of piston 16 and its connected parts and thus preventing overrunning of the said piston when adjustment of the valve is halted.

However, should it be desired to bring about rapid movement of piston l6 and valve 28 is adjusted rapidly, then a high pressure differential is set up between conduits 32 and 34 and this pressure difierential, via the pilot conduits I4, is impressed on valve member 52 thereby bringing about shifting of the valve member in one direction or the other into its by-passing position and thereby reducing the restriction offered to fluid flow to or from cylinder 14, thus permitting piston l6 and its connected parts to follow even the most rapid adjusting movements of the servo valve.

When the piston 18 and its connected parts approach the point where it is desired for them to come to rest movement of the servo valve will naturally be toward a position in which the piston will be slowed down. Movement of the servo valve to such a position will reduce the pressure differential between conduits 32 and 34, thus permitting valve member 52 to return to its centered position where it again creates a restriction in the fluid flow to or from cylinder [4, thereby damping movements of piston it and its connected parts, whereby they do not overrun when adjustment of the servo valve is finally halted.

In the foregoing it is seen by the use of the automatic restrictor valve, the servo-motor system can be made highly sensitive and quick acting so that the member moved at the output side of the system will respond immediately to the most minute adjustments of the servo valve and also follow the most rapid movements of the servo valve but, at the same time, the said parts will not overrun the servo valve at any time. Control over the parts moved at the output end of the servomotor is thus positive and continuous under all circumstances.

It will be understood that this invention is susceptible to modification in order to adapt it to difierent usages and conditions, and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. In a restrictor valve; a valve body, a pair of ports in said valve body, parallel flow passages in said valve body connecting said ports, a restrictor in one of said passages, a valve member normally closing the other of said passages when in a centered position and having opposite end positions where the said other passage is established, said valve member having stem portions extending out opposite ends of the valve body, spring means acting on said stem portions normally urging said valve toward its center position, a pilot cylinder enclosing each stem portion, and means for conveying pressure 'fluid to said pilot cylinders for acting on said stem portions, for moving said valve member toward one or the other of its end positions, said pilot cylinders including abutment means for prede terrrrining'the oppositeend positions of said valve member, .andi each iendiof sai'dvalve member comprising a tapered portionthat is disposed in the-mouth of said other passage when said valve member isshifted toward the pertaining end .position of the valve member whereby adjustment of .said abutment means will'determine the degree of restriction of saidother passage means when thervalve member is shifted.

2. In a restrictor valve; a valve body having a pair of ports, a central cavity in the body communicating with one of the ports, interconnected end cavities in the valve body in communication with the other port, a valve bore in the body leading from the end cavities to the central cavity, another bore in the body interconnecting the central cavity with the end cavities, a restrictor in said other bore, avalve member mounted in the said valve bore, said valve member comprising spaced spool portions in the said valve bore, and a central reduced diameter portion in said central cavity and tapering portions connecting the central portion with the said spool portions, said valve member comprising stems extending toward opposite ends of the valve body, pilot cylinders receiving said stems, springs in the cylinders acting on the stems normally urging the valve member to a centered position where it closes said valve bore and prevents communication between said central cavity and end cavities, and means for conducting pressure fluid to said cylinders for moving the valve member from its centered position to open the valve bore at one end or the other thereof to establish communication between said central cavity and said end cavities.

3, In a restrictor valve, a valve body having a valve bore, a valve member reciprooably mounted in said bore, chambers in said valve body at each end thereof intersecting said bore and hydraulically interconnected, said valve member having a center position where communication between said bore and chambers is interrupted, and having opposite end positions where said communication is established, means normally centering said valve member, fluid operable means for moving said valve member into either of its end positions, and a restricted channel continuously connecting said bore and chambers 4. In a restrictor valve, a valve body having a valve bore, chambers adjacent the ends of said. body intersecting said bore, said chambers being hydraulically interconnected, a first port in said body opening intosaid bore and a second port in said body opening into said chambers, means affording continuous restricted communication between said bore and chambers, a valve member in said bore having a center position where the ends of said bore are closed and having opposite end positions Where one or the other of the ends of said bore opens into the adjacent of said chambers, pilot cylinders on the ends of said body, said valve member having end parts extending into said cylinders, spring means in said pilot cylinders acting on the said end parts for normally centering said valve member, and means for conveying fluid pressure to said pilot cylinders for moving said valve member into its end positions against the influence of said springs.

5. In a restrictor valve, a valve body having a valve bore, chambers adjacent the ends of said body intersecting said bore, said chambers being hydraulically interconnected, a flrst port in said body opening into said bore and a second port in said body opening into said chambers, means affording xicontinuous :restricted communication between said here and chambers, a valve member- -in said-bore having a center position'where the ends of said bore are closed and having opposite endpositions where one or the other of "the ends of said bore opens into the adjacent of said chambers; pilot cylinders on the ends of said body, said valve member having end parts extending into said cylinders, spring means in said pilot cylinders acting on the said end parts for normally centering said valve member, and means for conveying fluid pressure to said pilot cylinders for moving said valve member into its end positions against the influence of said springs, there being adjustable abutment members in said cylinders for predetermining the end positions of said valve member.

6. In a restrictor valve, a valve body having a valve bore, chambers adjacent the ends of said body intersecting said bore, said chambers being hydraulically interconnected, a first port in said body opening into said bore and a second port in said body opening into said chambers, means affording continuous restricted communication between said bore and chambers, a valve member in said bore having a center postion where the ends of said bore are'closed and having opposite end positions where one or the other of the ends of said bore opens into the adjacent of said chambers, pilot cylinders on the ends of said body, said valve member having end parts extending into said cylinders, spring means in said pilot cylinders acting on the said end parts for normally centering said valve member, and means for conveying fluid pressure to said pilot cylinders for moving said valve member into its end positions against the influence of said springs, there being adjustable abutment members in said cylinders for predetermining the end positions of said valve member, and said valve member having a tapered portion at each end that is disposed in the end of the bore when the valve member is in its adjacent end position,

'7. In a hydraulic system; a reversible fluid motor, a pump, a servo-valve connected between the pump and. motor for reversibly controlling fluid flow to the motor, and a restrictor valve serially betweenthe motor and the servo-valve and comprising a normally open restricted channel and a normally closed channel by-passing said restricted channel, and means responsive to a predetermined pressure on either side of said motor for opening said normally closed channel.

8. In a hydraulic system; a reversible fluid motor having a pair of ports, a pump, a servo valve connected between said pump and the two ports of said motor for reversibly controlling the supply of fluid to said motor, and a restrictor valve serially connected between said motor and said servo-valve, said restrictor valve comprising a restricted channel normally connecting said servo-valve with the motor and a second channel by-passing said restricted channel, a valve member normally closing said second channel, and means responsive to a predetermined fluid pressure at either ot the ports of said motor for moving said valve member into position to open said second channel. I

9. In a hydraulic system; a reversible fluid motor having a pair of ports, a source of fluid pressure, a servo-valve connected to said source of pressure and having a pair of service ports connected with the ports of said motor for reversibly controlling of the supply of fluid to said motor, and a restrictor valve serially connected between said motor and said servo-valve comprising" a restricted channel normally connecting the servo-valve with the motor and a second channel Kay-passing said restricted channel, a valve member normally closing said second channel, and means responsive to a predetermined pressure at either of the service ports of said servo-valve for moving said valve member into position to open said second channel.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Robertshaw Sept. 22, 1931 Phelan Oct. 18, 1932 Kurtz et a1. Dec. 10, 1940 Millat Oct. 3, 1950 Walthers Jan. 8, 1952 Berhoudar Apr. 7, 1953 

